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Interfaces and implementations used by query node processors

<h2>Query Node Processors</h2>
<p>
The package <tt>org.apache.lucene.queryParser.processors</tt> contains interfaces
that should be implemented by every query node processor.
</p>
<p>
The interface that every query node processor should implement is {@link org.apache.lucene.queryParser.core.processors.QueryNodeProcessor}.
</p>
<p>
A query node processor should be used to process a {@link org.apache.lucene.queryParser.core.nodes.QueryNode} tree. 
{@link org.apache.lucene.queryParser.core.nodes.QueryNode} trees can be programmatically created or generated by a
text parser. See {@link org.apache.lucene.queryParser.core.parser} for more details about text parsers.
</p>

<p>
A query node processor should be used to process a {@link org.apache.lucene.queryParser.core.nodes.QueryNode} tree. 
{@link org.apache.lucene.queryParser.core.nodes.QueryNode} trees can be programmatically created or generated by a
text parser. See {@link org.apache.lucene.queryParser.core.parser} for more details about text parsers.
</p>

<p>
A pipeline of processors can be assembled using {@link org.apache.lucene.queryParser.core.processors.QueryNodeProcessorPipeline}.
</p>

<p>
Implementors may want to extend {@link org.apache.lucene.queryParser.core.processors.QueryNodeProcessorImpl}, which simplifies 
the implementation, because it walks automatically the {@link org.apache.lucene.queryParser.core.nodes.QueryNode}. See
{@link org.apache.lucene.queryParser.core.processors.QueryNodeProcessorImpl} for more details.   
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